Control for fluid operated motors



. -Aug. 7, 1945. Y c. J. KOPP k CONTROL FOR FLUID OPERATED MOTORS FiledAug. 11, 1943 4 Sheets-Sheet 1 J52 1/972 1 0 7": CarZJ/ZO Z 1 -c. J.KOPP CONTROL FOR FLUID OPERATED MOTORS 4 sheets sh'eet 2 Filed Aug. 11,1945 0 0' 5 Zw z Z w f m %z 7 W- W i "Hg W w 0 a a aw/Ma Z/ A 7 57 9 0w1 50 5 7 6 WM 4 i Q 7 V 3\ 6 a 7 a 5/ 5 a w 7 5 Z w 5\ 5- U F J n r 9 Z4 m fig 6 Z Aug. 7 1945. Q J KOPP 2,380,973

CONTROL FOR FLUID OPERATED MOTORS F298. I Fig.9 '79 82 45 5 7Y9 g5 55 l59 l w :2? 70 LL11 57415.? 841010672757 Aug. 7,1945. Q j KOPP I2,380,973

CONTROL FOR FLUID OPERATED MOTORS Filed'Aug. 11, 1945 4 Sheets-Sheet 462 Zawergizyg/ & 7 42527 Z Eatented Aug 7 1945 CONTROL FOB Um OPERATEDMOTORS Carl J. Kopp, Chicago, Ill., alsignor to Federal ElectricCompany, Inc., Chicago,- Ill., a corporation of New York ApplicationAngustll, 1943, Serial No. 493,139

7 Claims. (CI. -91),

This invention relates to control apparatus for fluid operated pistons,adapted to be utilized for controlling movement and/or positioningotvarious members or mechanisms, such as for example the height of aplaten of a press, or the bed of a, milling or boring machine. Moreparticularly the present invention is directed to apparatus forsimultaneously controlling the movement of a plurality of pistons whichare connected for moving various elements, or machines.

It has long been a problem to properly control the simultaneousoperation of a plurality of fluid actuated pistons when said pistons areutilized, as for example, for raising or lowering various elements orparts of a machine. The simultaneous operation of a plurality of pistonsnecessitates great care and skill, as well as the consumption of asubstantial amount of time.

One of the objects oi the present invention is to provide a novelcontrol for simultaneously operating a plurality of fluid operatedpistons for maintaining substantially synchronized or balanced movementof the piston elements.

Another object is to provide a novel control of the character indicatedwherein a main control valve is adapted to be actuated in directresponse to the differential of the rates of movement of twointerconnected pistons -fo'r proportionately varying the rate of flow offluid to the pistons, and thereby automatically causing "substantiallybalanced or equalized movement of thepiston elements.

A further obiect'is to provide an improved control of the characterindicated by virtue of which the rate of movement of a plurality oiinterconnected pistons serves to automatically effect adjustments of amain control valve so vas to maintain substantially uniform, balancedmovement of the piston elements.

Still another object is to provide 'a novel tw0-' directional fluidcontrol valve for a fluid system comprising a pair of cooperatingtelescoping valve elements, each connected to' a separate rotatableshaft, and'wherein a small amount of relative rotation of one shaft withrespect to the other instantly efl'ects adiustmentof the valve elementsby virtue of which said shafts are caused to rotate in substantialsynchronism with each other.

Other objects and advantages of this invention will be apparent from thefollowing description, taken in connection with the accompanyingdrawings in which:

Fig. 1 is a schematic illustration of my novel control apparatus for apair oi fluid operated pistons.

Fig. 2 is a vertical section through the control valve per se.

Fig. 3 is a section through the control valve, taken as indicated online 3-8 of Fig. 2.

Fig. 4 is a section through the'control valve,

drawings.

The control apparatus herein disclosed may utilize fluid in the tom ofgas or a liquid, and for purpose of illustration the present inventionwill hereinafter be described as being operated by liquid, such as oil.

In Fig. 1 of the drawings I have shown a pair of fluid operated motors,designated generally at it and ii, disposed in upright. position, eachcomprising a cylinder M; and a piston element ll, reciprocably movablewithin the cylinder id. The upper end of each piston rod It of thepiston elements is rigidly attached to a vertically disposed toothedrack it, mounted for slidable guided vertical movement, on the outerwall of the cylinder i4. Meshed with each of said racks is a pinion ll.Bald pinions are rigidly mounted on the outer ends of a pair of axiallyaligned, rotatable shafts ill and 2', which are operably associated witha main control valve designated generally at ii.

The control valve ii is constructed so as to maintain substantiallysynchronized or rotation of the two shafts I! and II and by virtue ofwhich the piston elements of the respective motors II and H are. causedto be raised or lowered in relatively synchronized relation to eachother. It is'to be imderstood that the upper ends of the piston rods I!may be operably connected to the machine bed or other object to be movedor supported thereby. The control valve is a hydraulically balanced unitand is operable by hydraulic pressure without having to overcome anyresistance caused by pressure within it. Such an arrangement isparticularly important if the control valve were operated by means otherthan racks and pinions, such as a cable and'drum, a Selsyn motor, orother meanswhich might not be capable of transmitting large amounts 01'power.

=1 atic illustration of the control apparatus represented in Fig. l ofthe As shown in Fig. 1 of the drawings, the upper ends of the chamberedportion of the cylinders ll are interconnected by a duct or conduit,formed-in two sections, as indicated at 2 and 25 which are joined to aconduit 26, connected to a conventional reversing valve indicatedgenerally at 21. The lower ends of the chambers of the cylinders areconnected by ducts or conduits 29 and 30, for the respective pistons land H, to the main control valve 2|. The main control valve isinterconnected with the reversing valve by a duct or conduit indicatedat 32. Oil is supplied to the system through the reversing valve 21, bya conduit 34. connected to a pump 35, driven by a motor 36, forsupplying oil through means of a conduit 38, from a storage tank 39. Thereversing valve 21 is also connected by conduit 40 to the storage tank39, to provide a return duct for the oil from the system to the sourceof upply.

The main control valve 2| includes a body 45 formed with a cylindricalbore 46 in which there is forcibly fitted a plurality of ringsdesignated at 41, 48, 49, 50,51 and 52 which are axially spaced apart byrings designated at 53, the internal diameter of which is substantiallygreater than the internal diameter of the other rings, so

a as to provide five annular chambers designated as 55, 58, 51, 58 and59. Snugly fitted within the bore 01' the rings 41 to 52 inclusive is apair of cooperating telescopic valve elements designated at 6| and 62.The valve element BI is in .the nature of a sleeve, formed as anintegral part of the shaft 20, and telescoped within the sleeve 61 isthe valve element 62, which is the terminal portion of the shaft 19. Thevalve.elements are maintained in position within the valve body by endplates 63, abutting against a shoulder formed at the rear end of thesleeve GI, and against a collar I9 fixed on the shaft IS. The valveelement 62 is formed with a pair of diametrically opposite,longitudinally extending passageways 65, which are in the form of keywayslots, terminating in approximate alignment with the outer walls of theend chambers 55 and 59.

The sleeve 8| is provided with four pair of axially spaced apart ports01, It, so and 10, with the ports of each pair disposed in diametricallyopposed relation to each other, as seen in Figs.

6, 8 and 9 inclusive of the drawings. When the shafts l9 and 20 arerotating in synchronized relation to each other, the ports 61 to 10inclusive are in semi-registration with the respective passageways 85 ofthe valve element 62. The ports 81 to 10 inclusive are open to anddisposed in registration respectively with the annular chambers 59, 58,n and 5!.

The sleeve Cl is also provided with a pair of diametrically oppositetransverse slots 12, located at substantially the center of the lengththereof,

that the chamber 5|, which is in registration with theports so, is inopen communication with a port 18, which is in one-way communicationwith a duct 19, connected to the conduit 29. A one-way ball check valvedesignated generally at 80 interconnects the port 18 and duct 19.

In Fig. 8 of the drawings it will be noted that the chamber 56, inregistration with the ports 69, is in direct communication with a portll, which in turn is connected to the duct 16, connected to conduit 30,with a one-way ball check valve, indicated generally at 82, interposedin the duct 8| so as to provide a one-way passage for the flow of oil inthe system. In Fig. 9 of the draw-- ings the chamber 55, in registrationwith the ports 10, is in direct communication with a port H, which' inturn is connected to the duct 19, with a one-way ball check valve,indicated generally at 85, interposed to provide a one-way passage offlow of oil.

For convenience, and for a more clear understanding of this invention,it may be here mentioned that the valve structure indicated in Fig. 5,controls the flow of oil to .eifect lowering of the piston element ofthe motor H The valve structure represented in Fig. 9, serves as thecontrol for the lowering of the piston element of the in registrationwith the annular chamber 51, so as to provide direct communicationbetween the pas sages l5 and a main port 11 formed in the valve body,and to which is connected the conduit .32.

The valve body is provided with separate ports and ducts forcommunication with the respective chambers inregistration with the ports61 to 10 inclusive. As may be seen in Fig. 5 of the drawings, thechamber 59, which is in registration with the valve port 01, opens intoa port 15, which is in one-way communication with a duct- 10, the latterbeing connected to the conduit 30.

'Interposed between the ducts II and I. is a one-way ball check valvedesignated generally at 11.- In Fig. 6 or the drawings it will be notedmotor. Ill, and the valve' arrangements represented in Figs. 6 and 8,respectivelv control the raising of the piston elements of the motors l0and I The reversing ,valve indicated generally at 21 may be understoodto be of the spring centered type and normally has ports thereof sodisposed that oil is caused to flow from the conduit 34.

directly into the conduit 40 so as to 'form a closed fluid system. Thereversing valve may be operated in any convenient manner, and as hereinshown by a pair of solenoids and 9 I. It is to be .understood that thesesolenoids may be separately and selectively energized by suitable switchmeans, not shown, for adjusting the reversing valve to either of twomain positions of adjustment. For example, it may be assumed that whenthe solenoid 90 is energized the ports of thereversing valve are soadjusted that oil is pumped through the conduit 34 into the conduit 32,through the main control valve 21, and through the conduits 28 and 30,to the lower ends of the cylinders H of said motors Iii and H, forraising the piston elements. In this position oi adjustment of thereversing valve, the conduit 20 is, then through a suitable portarrangement of the reversing valve, in direct communication with theexhaust conduit 40, so as to permitthe oil in the upper end of thecylinders, above the piston elements to be expelled. and returned to thestorage reservoir is. When solenoid I0 is deenergized and the othersolenoid II is energized, the reversing valve then assumes aposition ofadjustment wherein oil is pr nped through the conduit 84 into theconduit 20, and thence into the respective conduits 24 and II, into theupper ends of the chambers of the cylinders H, for causing lowering ofthe pistons I 5 within their respective cylinders. To accommodate suchlowering action the oil in the lower ends oi the chambers of thecylinders is caused to flow through the conduits 2e and 30 into the maincontrol valve II, from whence it flows through the conduit 32, whichwill then be-in direct communication with the exhaust conduit ll, torreturningfthe oil to the reservoir 30. The control valve ii, at thistime will tune-- tion to equalize the lowering of the pistons bycontrolling the exhaust oil from the cylinders.

It may be understood that if desired, suitable limit switches may beemployed for controlling the maximum and minimum position of adjustmentof the piston elements, which would correspond to the limits of movementof the members to be controlled by the pistons, such as the platen of 'apress, or the bed of a machine. Such limit switches could be connectedin series with the respective solenoids 90 and 9|, soxthat when thepistons arrived at their uppermost limit of adjustment, the actuatedsolenoid would be deenergized so as to permit the reversing valve 21, toagain assume its normal spring centered position of adjustment, at whichtime oil will then be pumped from the conduit 34 directly into theexhaust conduit 40, for return to the reservoir 39, and a properquantity of oil will be sealed in the system, so,as to support thepistons at such position of adjustment.

It is also to be understood that if desired the pump motor may becontrolled by relay circuits, connected incircuit with the respectivesolenoids and limit switches, so that the motor 36 functions only whenone of the solenoids is energized and the limit switches are closed.

Operation of control valve valve, reading from right to left, correspondto the sections disclosed respectively in Figs. 5 to 9 inclusive.

If it be assumed now that the reversing valve der of the motor In, anda. reduced. quantity of oil would be supplied to the lower end of thecylinder of motor II. By virtue of this arrangement the two motors arealmost instantly brought into synchronized adjustment, or relationship,so that they constantly tend to move in equalized or balanced relationto each other.

When the piston elements of the respective motors in and H are caused tobe lowered by the readjustment of the reversing valve 21, by actuationof solenoid 9|, as above described, the oil is supplied through theconduit 34, directly into the conduit 26, for feeding the oil throughthe conduits 24 and 25, into the upper end of the cylinder chambers. Theoil at the bottom of the chambers, below the piston elements, is thenforced through the respective conduits 29 and 39 into the main controlvalve 2| and the oil from the conduit 29 passes through the ball checkvalve 85, through the duct 94 into the chamber 55, surrounding the ports10 through which the oil then feeds into the passageways 65, and the oilfrom the conduit 30 feeds into the duct 16, and through the one-waycheck valve 11 and duct I5 into the chamber 59, surrounding the ports61, and then discharges into the passageways 65. The oil is thendischarged from the passageways through the slots 12, port 13 intoconduit 32, for return through the reversing valve 21, to the storagesupply tank 39.

In the event one of the piston elements tends to travel downwardly at arate of speed, in excess of the other, it will result in relativerotation of the shafts I9 and 20 with respect to each other,

21 is adjusted by actuation of solenoid 99, so as to cause raising ofthe piston elements in their respective cylinders, the oil is suppliedfrom'the conduit 94 directly to the conduit 32,.and enters the chamber51 of the main control valve. Oil then flows into slots 12 of the sleevevalve element Bl, into passageways 65, in the inner valve element 62,from whence it flows through the ports 68 and 69 (see Figs. 6' and 8),into the chambers 58 and 56, into the respective ducts 19 and 8| whichare in direct one-way communication with the conduits 29 and 30respectively,

so as to supply oil to the lower portion of the cylinders of therespective motors Ill and II. It will be noted that at this time oilcannot flow through the ports 61 and 10 because of the one-,

way ball check valves" and 85. When the reversing valve is so adjustedthe oil 'at the upper ends of cylinders I4 is permitted to returnthrough the conduits 24, 25, and through the conduit 26, to theexhaustconduit 40, for return to the'storage reservoir 39. If during theraising action of the two pistons one of the pistons tends to travelfaster than the other, as for example the piston element in the motorII, this will cause the shaft 20 to rotate a slight amount relatively tothe shaft l9. This, as ay be observed from Fig. 6 of the drawings, wo'to rotate, in countercloc direction, slightly in excess of the rate ofrotation of the valve 'element 62, which would cause the ports 88 toincrease their registration with the passageways 65, while at the sametime it would cause the ports 69, as seen in Fig. 8 of the drawings, todecrease the extent of their registration with said passageways 95. Thusa greater proportion and by virtue of which adjustment of the ports 61and 10 with respect to the passageways 65 is effected in the same manneras above described in connection with the raising of the pistons, thatis, the main control valve 2| becomes adjusted for proportionatelyincreasing the flow of oil from the piston which is moving the slower ofthe two, while at the same time reducing the quantity of oil flowingfrom the other piston which is traveling at the higher rate of speed.During the lowering operation oil cannot flow through the ports 68 and69 because of the oneway ball check valves 80 and 82.

It will be noted that full oil pressure is exerted I maybe so limited bythe appended claims.

cause the sleeve z iil of the available oil supplied through the duct Iclaim as my invention: 1. In combination with a fluid operated motorcomprising a cylinder and a piston element reciprocably movable in thcylinder, a controlv for the motor comprising a toothed rack,connectedto and movable with the piston element, a pinion meshed withand rotatable incident to such movement of the rack, a control valvecomprising a body provided with a main port and spaced apartinlet andoutlet ports, check valves in said inlet and outlet ports to permitpassage of fluid in only one direction therethrough, two

I do not, therefore, wish to shafts, one of said shafts having aterminal portion extending into said valve body and constituting a valveelement, said shaft portion being provided with an elongated passageway,a sleeve connected to the adjacent end of the other shaft and disposedin said body in surrounding relation to said shaft portion, said sleevebeing provided with axially spaced apart inlet and outlet ports normallydisposed in registration with said passageway and an opening to providedirect communication between said passageway and main port, said valvebody having internal chambers to provide communication between saidinlet and outlet ports of the sleeve and the,

corresponding inlet and outlet ports of the body, one of said shaftsbeing rigidly connected to said pinion, a source of liquid supply, apump connected to said supply, a reversing valve, duct means connectingthe pump to the reversing valve, duct means connecting the reversingvalve and main port of the control valve, duct means connecting thereversing valve to one end of said cylinder, duct means connecting theopposite end of the cylinder to the inlet and outlet ports of the valvebody, and duct means connecting the reversing valve to the source offluid supply, whereby the adjustment of the reversing valve to oneposition, during synchronized relationship of said shafts, causes fluidto enter one end of the cylinder to move the piston element andsimultaneously causes the fluid at the opposite end of the cylinder toreturn to said source of fluid supply, and adjustment of the reversingvalve to another position, during synchronized relationship of saidshafts, causes fluid to enter said opposit end of the cylinder to movethe piston in an opposite direction and causes the fluid at said one endof the cylinder to return to said source of fluid supply.

2. In combination with a fluid operated motor comprising a cylinder anda piston element reciprocably movable in the cylinder, 9, control forthe motor comprising a toothed rack, connected to and movable with thepiston element, a pinion meshed with and rotatable incident to suchmovement of the rack, a control valve comprising a body provided with amain port and spaced apart inlet and outlet ports, check valves in saidinlet and outlet ports to permit passage of .fluid in only one directiontherethrough, two oppositely extending axially aligned rotatable shafts,one of said shafts having a terminal por tion extending into said valvebody and constituting a valve element, said shaft portion being providedwith two circumferentially spaced apart longitudinallyextendingpassageways, a sleeve connected to the adjacent end of theother shaft and disposed in said body in surrounding relation to saidshaft portion, said sleeve being provided with dual sets of axiallyspaced apartinlet and outlet ports normally disposed in registrationwith said passageways and an opening to provide direct communicationbetween said passageways and said main port, said valve body having;internal chambers providing communication between the dual sets of inletand outlet ports of the sleeve and the corresponding inlet and outletports of the body, one of said shafts being rigidly connected to saidpinion, a source of fluid supply, a pump connected to ,said supply, areversing valve, duct means connecting the pump and reversing valve,

duct means connecting the reversing valve and oppositely extendingaxially aligned rotatable necting the'reversing valve to one end of saidcylinder, duct means connecting the opposite end of the cylinder to theinlet and outlet ports of the valve body, and duct means connecting thereversing valve to the source of fluid supply, whereby the adiustment ofthe reversing valve to on position, during synchronized relationship ofsaid shafts, causes fluid to enter one end of the cylinder to move thepiston element and simultaneously causes the fluid at the opposite endof the cylinder to return to said source of fluid supply, and adjustmentof the reversing valve to another position, during synchronizedrelationship of said shafts, causes fluid to enter said opposite end ofthe cylinder to move the piston in an opposite direction and causes thefluid at said one end of the cylinder to return to said source of fluidsupply.

3. A two direction fluid control valve comprising a body provided with amain port and spaced apart inlet and outlet ports, check valves in saidinlet and outlet ports to permit passage of fluid in only one directiontherethrough, two oppositely extending axially aligned shafts, oneofsaid shafts having a terminal portion extending into said valve body andconstituting a valve element, said shaft portion being provided with anelongated passageway, and a sleeve connected to the adjacent end of theother shaft and disposed in said body in surrounding relation to saidshaft portion, said sleeve being provided with two sets of axiallyspaced apart inlet and outlet ports adapted to be disposed insubstantially semiregistration with the passageway and a separateopening providing direct communication between said passageway and saidmain port, said valve body being provided with internal chambersproviding communication between said inlet and outlet ports of,thesleeve and the corresponding inlet and outlet ports of the body, wherebya small amount of relative rotation of one shaft with respect to theother in one direction, during either direction of flow of the fluid,increases the effective registration of one set of inlet and outletports of the sleeve with the passageway and decreases the eflectiveregistration of the other set of inlet and outlet ports of the sleevewith said passageway, and opposite relative rotation of said shafts,during either direction of flow of the fluid, decreases the effectiveregistration of said one set of inlet and outlet ports of the sleevewith the passageway and increases the effective registration of saidother set of inlet and outlet ports of the sleeve with said passageway.4. A two direction fluid control valve comprising a body provided with amain port and spaced apart inlet and outlet ports, check valves in saidinlet and outlet ports to permit passage of fluid in only one directiontherethrough, two oppositely extending axially aligned shafts, one ofsaid shafts having a terminal portion extending into said valve body andconstituting a valve element, said shaft portion being provided with twocircumferentially spaced apart longitudinally extending passageways, anda sleeve connected to the adjacent end of the other shaft and disposedin said body in surrounding relation to said shaft portion, said sleevebeing provided with two sets of axially spaced apart inlet and outletports normally disposed respectively in substantially semi-registrationwith said passageways and a separate opening providing directcommunication between said two passageways and said main port, saidvalve body being provided with internal chambers providing communicationbetween the sets of inlet and outlet ports of the sleeve with thecorresponding inlet and outlet ports of the body, whereby a small amountof relative rotation of one shaft with respect to the other in onedirection, during either direction of flow of 5 the fluid, increases theeffective registration of one set of inlet and outlet ports of thesleeve with said passageways and decreases the effective registration ofthe other set of inlet and outlet ports" of the sleeve with saidpassageways, and opposite relative rotation of said shafts, duringeither direction of flow of the fluid, decreases the effec-. tiveregistration of said one set of inlet and outlet ports of the sleevewith said passageways and increases the efiective registration of saidother set of inlet and outlet ports of the sleeve with said passageways.

' 5. In combination, a pair of spaced apart hydraulically actuatedmotors each comprising a cylinder and a piston element reciprocablymovable therein, two sets of liquid ducts connected 1 respectively tocorresponding ends of the respective cylinders, an equalizing valveconnected in one set of ducts, a reversing valve connected in the otherset of ducts, a duct interconnecting the equalizing valve and reversingvalve, means for supplying liquid, from a source of supply, underpressure to said reversing valve, a return duct connecting the reversingvalve to the source of supply, said reversing valve being adapted in oneposition of adjustment to supply liquid under pressure to acorresponding end. of each of said cylinders and causing the liquid atthe opposite ends to' return to the source of supply, and

adapted in another position of adjustment to supply liquid underpressure to said opposite ends of the cylinders and causing the liquidat said corresponding end of each cylinder to return to the source ofsupply, said equalizing valve comprising two relatively rotatable valveelements 40 for controlling the flow of liquid to and from correspondingends of the cylinders and between said equalizing and reversing valves.and meanz operably connecting said valve elements to respective pistons,said elements being adjustable relatively to each other in response tothe difierential of the rate of movement of said pistons forproportionally varying therate of flow of the equalizing valve .andreversing valve, means for 60 supplying liquid. from a source 01'supply, under pressure to said reversing valve, a return duct connectingthe reversing valve to the source oi! supply, said reversing valve beingadapted in one able therein, two sets ofliquid ducts connected positionof adjustment to supply liquid under pressure to a corresponding end ofeach of said cylinders-and causing the liquid at the opposite ends toreturn to the source of" supply, and adapted in another position ofadjustment to supply liquid under, pressure to said opposite ends of thecylinders and causing the liquid at said corresponding end of eachcylinder to return to the source of supply, said equalizing valvecomprising two relatively rotatable valve elements telescopedone withinthe other and provided with suitable ports for communicating with saidone set of ducts and with. the said duct interconnecting the equalizingvalve and reversing valve, and means operably connecting said valveelements to the respective pistons, said elements being adjustablerelatively to each other in response to the differential of the rate ofmovement of said pistons for proportionally varying the rate of flow ofthe liquid to or from corresponding ends of said cylinders, whereby tocause substantially equalized movement of said pistons.

7. In combination, a pair of spaced apart hydraulically actuated motorseach comprising a cylinder and a piston element reciprocably movabletherein, two sets of liquid ducts connected respectively tocorresponding ends of the respective cylinders, an equalizing valv'econnected in one set of ducts, a reversing valve connected in the otherset of ducts, a duct interconnecting the equalizing valve and reversingvalve, means for supplying liquid, from a source of supply, underpressure to said reversing valve, a return duct connecting the reversingvalve to the source of supply, ,said reversing valve being adapted inone position of adjustmentto supply liquid under pressure to acorresponding end of each of said cylinders and causing the liquid atthe opposite ends to return to the} source of supply, and

adapted in another position of adjustment to' supply liquid underpressure to said opposite ends of the cylinders and causing the liquidat said corresponding end of each cylinder to return to the source ofsupply, said equalizing valve comprising two relatively rotatable valveelements telescoped one within the other and providedv with suitableports for communicating with said vone set of ducts and with the saidduct interconnecting the equalizing valve and reversing valve. a toothedrack extending longitudinally of each cylinder and operably connected tosaid pistons for movement therewith, a pinion meshing with each rack,and a pair of axially aligned shafts connected at corresponding ends tosaid pinions, and their opposite, adjacent ends being fixedly connectedto the respective :valve elements, whereby the difl'erential rate ofmovement or said pistons eflects relative rotative adiustment'oithevalve elements for proportionally varying the rate of flow of liquid toor from said corresponding ends or the cylinders to cause substantiallyequalized movement or said pistons.

' 'cruu. J. Kora

